Electronic devices having liquid crystal displays (LCDs), such as personal digital assistants (PDAs), have complex circuit configurations including a plurality of circuit blocks to perform various functions of the electronic device. A plurality of voltages having different levels may be required for the circuit blocks. Hence, a power voltage supplied from the outside may be boosted to generate the plurality of voltages having the different levels in the electronic devices.
The plurality of voltages are typically sequentially boosted for stable operations of the electronic devices when the electronic devices are powered on. Points in time (durations) when a plurality of voltages are generated, i.e., time intervals between points in time when a plurality of voltages are generated, can be obtained by adding the optimum time interval obtained by simulation and a margin obtained by considering stability. As a result, in a case where the number of voltages to be boosted increases, the time taken from the power-on to generating of the last boosting voltage increases. In addition, the optimum time interval may be changed according to process characteristics of the electronic devices and their surrounding environments. The cost and time for obtaining the optimum points for generating boosting voltages through simulations and tests increase.